As-built drawings: why the last drawing set matters most

The as-built set is the last issue of a project and usually the one a building keeps longest. Every other drawing in the set describes an intention. The as-built drawings describe what is actually there, which is what anyone returning to the building needs to know.

Installations move

Installations commonly depart from the drawings in small ways, and the reasons are rarely failures of the design. Site conditions are not fully known when a set is issued, and a building keeps changing while it is being built:

• A pathway is rerouted around structure or a service discovered on site
• A device shifts to clear a diffuser, a beam or a door swing
• An equipment substitution arrives with a different footprint or connector
• A cable is re-terminated, relabelled or pulled through different containment
• A room changes use late in the programme and takes its audio-visual provision with it

Each of those is a small and reasonable decision on the day. Together they account for the difference between the set issued for construction and the building as it stands.

What the as-built set records

• Final device positions on floor plans and reflected ceiling plans
• The system schematic updated to the signal flow as installed
• Rack layouts and rack elevations showing the equipment as it was fitted
• The cable schedule updated with the terminations and labels that exist
• Equipment manufacturer and mounting detail for what was installed rather than what was specified

Who reads it, and when

We prepare the as-built set for readers who are not in the room when it is issued. It is generally consulted later in the life of the building, often by people who were not on the project:

• The maintenance team tracing a fault back to a rack position or a cable label
• The team extending the system, who need to know what capacity is already used
• The designer of the next project in the building, who has to work around what exists
• The client’s own records, where the set is the evidence of what was delivered

Those readers may have nobody left to ask, so we draw the set on the assumption that it has to answer on its own.

Capturing it while it can still be captured

As-built information is easier to collect while the installation is fresh. The method is unglamorous. The set that goes to site comes back marked up, and marked-up prints, photographs and site notes are gathered as the work proceeds rather than reconstructed from memory at the end.

It helps when the drafter who prepared the original set prepares the as-built issue as well. Somebody who drew the schematic knows what a change on site actually alters. They can carry it through the plan, the schedule and the rack elevation, instead of correcting one drawing and leaving the others behind. That is one reason projects stay with the same personnel here, from initial scope through to final submission.

Keeping the last set usable

An as-built set is most useful when it reads like the rest of the documentation: the same layers, the same title blocks, the same naming, the same conventions. A set corrected in a hurry, in a different style, by whoever happened to be free, gives the next reader a reason to doubt it and redraw it.

That consistency is the purpose of CAD standards and management, and it applies to the last issue of a project as firmly as to the first. The as-built drawings are also where audio-visual system design ends, which is why we treat them as part of the design work rather than as paperwork that follows it.